1. Field of the Invention
This invention generally relates to sound generation, and more particularly to a method for controlling a synthesizer to produce a desired sound.
2. Description of the Related Art
Sound synthesis systems have been known for years. These systems generate sound by controlling one or more of the frequency and timbral characteristics of an initial signal. Early sound synthesizers generated sound by adjusting just a few parameters to control equalization characteristics (e.g., base and treble) of a reference signal. As technology progressed, so did the level of complexity of sound synthesis control. Today, literally scores of parameters are considered for adjustment.
While sound synthesizers have a variety of uses, there is, perhaps, no more common application than to the synthesis of musical sounds. Musical sound synthesis requires controlling an input reference signal over a wide dynamic range in order to accommodate the frequency characteristics of the different instruments forming the music.
Piano and guitar tones, for example, rise quickly to an initial maximum, then gradually decay. Orchestral instruments, on the other hand, dampen quickly when playing ceases. Further, many musical tones have characteristic transients which greatly influence timbre. In organ tones, for example, the transients are of different fundamental frequencies, and they tend to appear and decay before steady state is reached. In percussive tones, on the other hand, the initial transient is the cause of the tone and the final transient is the result.
Other applications of sound synthesis technology include speech synthesis, ambient sound reproduction, and sound effects generation as, for example, in video games, movies, and other forms of entertainment. Sound synthesis has also been used-to advance a number of military objectives.
Sound synthesizers may be digital or analog. One type of digital synthesis technique is sample-based synthesis, which has been in existence for nearly twenty years under various names including "sample playback" and "wave table" synthesis. Sample-based synthesizers produce sound by playing back stored digital recordings. The playback is digitally "sped up" or "slowed down" to alter pitch, thereby allowing a single recording to be used for a range of pitch playback. Further, to generate sustained notes for periods of time longer than on the recording, a technique is employed to "loop" a portion of the sample.
FIG. 1 shows a conventional sample-based synthesizer 100 equipped with time-varying filters 101, modulators 102, and oscillators 103. In operation, the synthesizer controls these elements to generate a synthesized output that can very closely mimic a non-synthesized sound. If the input digital sample is of an instrument, for example, the synthesizer will adjust the parameters of one or more of its filters, modulators, and oscillators to generate a sound mimicking playing of the instrument, with all its attendant dampening and sustaining characteristics.
The quality of sound generated by a digital synthesizer is dependent upon a number of factors. First and foremost is the quality of the digital samples themselves, which serve as references for the synthesis. Increasing the quality of digital samples is one technique that can be employed to improve sound synthesis. There are, however, countervailing considerations to this approach. As is always the case in digital recordings, a balance between storage space and desired quality must be struck. Factors such as sampling frequency, sample word-length, length of the sample, and number of samples used are all critical. For example, 30 seconds of 24 bit samples at 96 kHz will make for a much better quality sound than 5 seconds of 8 bit 22.1 kHz samples, but the former will also substantially increase the storage requirements of the synthesizer.
Another factor affecting the quality of sound from a digital synthesizer is the selection of loop points. A careless selection of loop points can result in a buzzing or clicking effect. Further, to convey the timbre of the instrument, a long enough sample segment must be looped. The longer the loop, however, the more of the sample which must be stored. Thus, it is clear that, along with other factors, the length of the loop affects the memory requirements of the synthesizer.
Another factor is the filters and modulators used to generate the sound. These circuits are typically controlled in order to mimic the natural decay of the sound of an instrument in the synthesized output. Use of such filters applied during the looped portion of the sample playback, for example, can allow for a much shorter sample loop while still maintaining a faithful reproduction of the sound of the instrument. Decay, reverberation, and other effects are also generated through control of these circuits.
One of the latest incarnations of sound synthesizers is their embodiment in software for use on a computer. Examples include "Reality" by Seer Systems and "Creative WaveSynth/WG" by Creative Labs. Wave-table synthesis cards, such as the Creative Labs AWE64, have also been developed. Typically, these devices are controlled by software on a personal computer and serve as standard or inexpensive optional equipment with greatly reduced storage and bandwidth capabilities. With careful programming, however, wave-table synthesis cards can do a credible job at many synthesis tasks. For example, these cards have found particularly useful application when used with gaming and entertainment software. Microsoft, through their Direct Music API, supports the Downloadable Sound ("DLS") standard to serve such a purpose.
Conventional sound synthesizers have a number of drawbacks. Perhaps most significantly, these systems rely on a completely manual process to design a synthesized sound, or "patch." The skill and experience of each individual technician, thus, almost invariably dictate the quality of output of the synthesizer.
To generate the multiple synthesized sounds typically offered on musical sound synthesizers today a technician must manually adjust the parameters of the synthesizer to produce, in his best estimation, an output which most closely mimics a sound. This at least requires a thorough understanding of the structural and function configuration of the system, and how the various features therein may be interrelated to produce sound. Since the number of parameters considered for adjustment often number 50, 60, or more, this becomes a complex and tedious endeavor. As an example, the Kurzweil 2500S synthesizer is a sample-based sound synthesizer which mimics various musical instruments by allowing for adjustment of over a hundred parameters, each of which directly impacts the resulting sound.
The combination of artistic and technical skills required to program a sample-based synthesizer, thus, has, almost by necessity, relegated synthesis patch design to a "black art," with relatively few skilled practitioners. Lay users are, for all intents and purposes, excluded from such an undertaking, since it would likely take them hours to, one, familiarize themselves with the operation and configuration of the synthesizer, and, two, adjust the likely scores of parameters required to generate a high-quality synthesized sound.
It is therefore apparent that a need exists for a method of controlling a synthesizer, digital or analog, to generate sound in a more efficient and less costly manner compared with their conventional counterparts, and moreover one which allows lay persons to program a synthesizer to generate customized sounds of a quality at least equal to that attainable by a skilled technician practicing conventional manual methods.